Water is a valuable resource, particularly for space exploration, and it is obviously necessary for human habitation. Extraction of water from planetary bodies is desirable for human life support, for radiation protection shielding and as propellant. Water and a number of other useful volatiles may exist on the moon and other planetary bodies. Water can easily be electrolyzed (with solar or nuclear energy) into hydrogen and oxygen. This hydrogen and oxygen can be stored and subsequently used with fuel cells for electrical energy or as a propulsion fuel. Water is present in comets as well as on the surface of planetary bodies (e.g., Mars, the moon). This water can be extracted for utilization during space exploration activities.
Simple and cost-effective extraction of water and subsequent electrolyzing would enable the development of a fuel depot in space, on the moon, or on other planetary bodies. The resulting fuel would have commercial, military, and NASA uses. The efficient extraction of water or other volatiles would permit the return of spacecrafts from planetary bodies without having to launch the return fuel from Earth.
Volatile species are often found below the soil surface, with the highest concentration often a distance from the surface. Applying microwaves to the surface results in the greatest heating at the surface and spreads (with decreasing heating effect) deeper into the surface as the microwave energy is attenuated in the soil. The lunar surface has a low thermal conductivity, which strongly disfavors traditional methods of heating. Microwave heating of regolith is faster and more efficient than other heating methods due to the ability to couple energy into the subsurface volume.
In addition, microwaves can penetrate into the soil permitting water removal from deep below the surface with collection above the surface. This permits the extraction of water or other volatiles without the need to dig or excavate the surface.
The desired wavelength of the microwaves may be adjusted for the electromagnetic properties of the regolith (e.g., lunar, Martian, Earth, asteroid).
The delivery of microwave energy into soil from the earth's surface is known. Microwave heating, particularly of lunar regolith, is potentially faster and more efficient than other heating methods due to the very low thermal conductivity of lunar regolith. This is especially true in the vacuum on the moon and in the low partial pressure of Mars. For example, U.S. Pat. No. 4,571,473 (Wyslouzil '473) describes a microwave applicator for thawing frozen ground using a coaxial line to deliver microwaves into the ground.
U.S. application Ser. No. 11/477,253 (Taylor '253) describes an apparatus and method for in-situ microwave consolidation of planetary materials containing nano-sized metallic iron particles to sinter and/or melt the particles for use in roadways and other construction materials. Taylor '253 uses a generator, waveguide, and funnel to generate and direct microwave energy from a paver to a particulate surface under the paver to heat and consolidate the lunar soil particles into a suitable solid mass.
The method taught by Taylor '253 relies on the presence of iron in nanophase metallic iron-containing particles to generate the heat necessary to sinter and/or melt the particles. However, the precise quantity and location of nanophase iron or other metals in lunar regolith is unknown; therefore, is it undesirable to rely on an apparatus or method that requires iron.
It is desirable to have a device which utilizes microwaves to extract and collect volatiles from regolith.
It is desirable to have a device for extracting and collecting volatiles from regolith that does not require digging, drilling, excavating, or removal of overlying soil.
It is desirable to have a system for efficient and cost-effective extraction and collection of volatiles from regolith for use or further processing.
It is desirable to have a device for heating regolith which does not rely on the presence of iron.
It is desirable to have a device for extracting and collecting volatiles from regolith that can be adjusted for regolith having various electromagnetic properties.
It is desirable to have a device capable of extracting and collecting volatiles without having to thaw the regolith.
It is desirable to have a device for extracting and collecting volatiles that heats soil to a significant depth without relying on thermal conduction, convection, or thermal radiation.
It is desirable to have structurally integrated components, which minimize the number of parts that must be manufactured and tested.